netdev - Re: [BUG] net/sched: Soft Lockup/Task Hang and OOM Loop in netem

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Message-ID: <FiSC_W4LweZiirPYQVe8p7CvUePHrufeDOQgkDT07zh-uy5s6eah-a8Vtr_lPrW73PAF51p6PPIrJITwrJ5vspk99wI5uZELnJijU5ILMUQ=@willsroot.io>
Date: Sat, 24 May 2025 20:09:11 +0000
From: William Liu <will@...lsroot.io>
To: Jamal Hadi Salim <jhs@...atatu.com>
Cc: "netdev@...r.kernel.org" <netdev@...r.kernel.org>, Savy <savy@...t3mfailure.io>, Cong Wang <xiyou.wangcong@...il.com>, Victor Nogueira <victor@...atatu.com>, Pedro Tammela <pctammela@...atatu.com>, Paolo Abeni <pabeni@...hat.com>, Jakub Kicinski <kuba@...nel.org>, Stephen Hemminger <stephen@...workplumber.org>, Davide Caratti <dcaratti@...hat.com>
Subject: Re: [BUG] net/sched: Soft Lockup/Task Hang and OOM Loop in netem_dequeue

On Saturday, May 24th, 2025 at 1:07 PM, Jamal Hadi Salim <jhs@...atatu.com> wrote:

> "count == 0" seems to be only needed for the loss when a drop decision is made.
> Slight tangent: Looking at init() the setup does allow for both to be
> on (i.e could be "and" not just "or" as you state above). It feels
> sensible to me that if the loss function decided the packet is to be
> dropped then that would override the duplication.

This makes perfect sense to me.

By that, I agree that the count variable is not necessary. However, I think it's good to introduce a duplicated boolean instead for readablity's sake, instead of merging all the logic into nest_level. I will get a formal patch set ready sometime soon to address the bug and the other behavioral quirks we found here. 

Thank you for the help so far!